1. Field of the Invention
This invention relates to the field of sealing joints, in particular those that ensure sealing at the level of and around a movable element, such as a shaft, an axle or the like, driven by a rotational movement and extending in or through a passage, a housing, an opening or the like of a stationary body, element, casing or the like.
2. Description of the Related Art
More particularly, the invention relates to a sealing joint comprising, on the one hand, a support ring or frame (generally made of steel plate) with an external axial flange and an internal radial flange, and, on the other hand, a washer made of a TEFLON®-based sealing material, which is mounted or arranged on said ring, by at least partially covering the external surface of the axial flange and extending beyond the inner end of the radial flange in such a way as to form a flexible sealing lip. This lip is designed to be applied circumferentially against or on an element that is to be sealed, in particular a rotational cylindrical element such as a shaft or the like, with said sealing lip then having a first annular portion that for the most part rests on the element that is to be sealed and a second annular curved connecting portion (connecting the first end portion of the lip to the part of the washer made integral with the radial flange of the ring).
Such a joint is known in particular by the documents WO 2008/009317 and US 2003/0031828 (FIG. 5a).
These joints ensure, with the same washer, a double-seal, namely both an internal dynamic seal relative to the movable element (by means of the flexible sealing lip that is not supported by the ring) and an external static seal relative to the wall of the housing or the mounting opening, through which the element that is to be sealed generally passes (by means of the washer part present on the external surface of the axial flange).
However, the sealing joints disclosed by these two documents have at least the following two drawbacks:
1) A lifting of the free end of the sealing lip whose effect is negative in terms of maintaining tightness and sealing behavior is noted, in particular when this lip rests on the element that is to be sealed over a great length (significant axial distance);
2) These joints are not suitable for withstanding pressure (problem of sealing behavior at the level of the element that is to be sealed when the medium that is to be isolated contains pressurized liquid, typically between approximately 1 and 10 bar), because of a low resistance to deformation, and even a possible turning of the sealing lip when the latter is subjected to pressure (for example, in applications such as sealing pump shafts).
To attempt to remedy these two drawbacks, the document US 2002/0117810 proposes a sealing joint whose sealing lip has a significant thickness and is subdivided radially into a primary sealing lip, coming to rest on the element that is to be sealed, and a secondary elastic support lip.
This secondary lip comes (in the absence of significant pressure) into contact with the free end (tip) by exerting a support force stressing this end against the element that is to be sealed and thus combating its separation and its lifting.
In addition, when the medium that is to be isolated is subjected to pressure, the primary and secondary lips are superposed tightly and together form a single lip of great thickness that can withstand pressure without turning.
However, although providing satisfaction when the lip/element contact area has a short distance, this solution is complex structurally and its achievement is difficult (requiring a precise cutaway of the lip, double-machining of the primary and secondary lips).
In addition, the material cost is high, taking into account the large thickness of the bottom lip, and the friction forces between the lip and the movable element are increased.
Finally, in the document US 2002/0117810, the external static seal (between joint and housing) is obtained by using a second sealing material.